The invention is directed to an adjustable mount of the type shown in DE 44 00 869 C1 for optical components.
An apparatus is known from U.S. Pat. No. 6,876,494 B2 by which light is projected in a predetermined pattern onto a wafer in that the light is spatially modulated via microoptical elements. It is important for the quality of the modulation that, inter alia, a microlens array associated with the apparatus be aligned in a highly accurate manner with a complementary pinhole array which is arranged behind the microlens array in direction of the optical axis.
The apparatus disclosed in U.S. Pat. No. 6,876,494 B2 is based on a prior art which is described in JP 2001-21830 according to which a pinhole array is positioned relative to a microlens array in an apparatus of the type mentioned above. It is stated that the microlens array used in JP 2001-21830 comprises microlenses with a low numerical aperture and a focal length of 5 mm, which explains why an exact positioning in direction of the optical axis is not a consideration.
However, if a microlens array with microlenses of a high numerical aperture and a focal length of approximately 250-300 μm is used, it is necessary to position the pinhole array relative to the microlens array in direction of the optical axis in a highly accurate manner so that the individual light components bundled through the microlenses are focused into the pinholes.
In order to position the microlens array and the pinhole array at an exactly predetermined distance relative to one another, it is suggested in U.S. Pat. No. 6,876,494 B2 to form on the microlens array or on the pinhole array at least one protrusion toward the other array, which protrusion has a predetermined height in direction of the optical axis and determines the spacing of the arrays. In this way the position of the arrays can be exactly adjusted relative to one another in direction of the optical axis.
Instead of the at least one protrusion, a spacer having a predetermined thickness could also be inserted between the microlens array and the pinhole array. No information can be gathered from U.S. Pat. No. 6,876,494 B2 with regard to the need for accurate positioning also perpendicular to the optical axis (lateral positioning). However, it is clear that a lateral adjustment of the two arrays with indirect contact via protrusions or a spacer is subject to friction. A sensitive, deterministic adjustment on the order of 0.05 μm such as is aimed for by the present applicant is made more difficult by the stick-slip effect.
Adjustable mounts for optical components allowing a lateral adjustment, i.e., an adjustment in a plane perpendicular to the optical axis of an optical system, generally have an outer mount part which is fixedly connected to the housing of the optical system, or is a component part of the housing, and an inner mount part which carries the optical element and can be displaced and rotated relative to the outer mount part in the plane by means of adjusting elements.
In some known adjustable mounts, the mount parts are individual parts that must be fixed relative to one another after the adjustment; in other known adjustable mounts the mount is produced monolithically and the mount parts remain in the adjusted position in a self-locking manner without needing to be fixed. Generally, the first type of mount is used for larger adjustment paths with less sensitivity and the second type of mount is used for small, highly sensitive adjustment paths.
An adjustable mount (in this case, an arrangement for lateral adjustment of lenses within a high-performance objective) in which the mount parts are individual parts is known from DE 44 00 869. The mount comprises an inner mount part (lens mount) and an outer mount part (first mount) which are connected to one another by a releasable, frictionally engaging, axially acting clamping device.
The inner mount part in which the lens is supported is held in the outer mount part, which is fitted into an objective housing, by pressing forces which act exclusively parallel to the optical axis of the objective and which are partially compensated perpendicular to the optical axis during a lateral adjustment by counterforces which are generated by piezoelectric translators arranged in the inner mount part, so as to make possible a lateral displacement of the inner mount part within the outer mount part with a small radial force.
The outer mount part has an inner plane face against which the inner mount part is pressed by pressing means. A pressing ring which is fixedly connected to the outer mount part, a spring ring and an adapting ring contacting the inner mount are advantageously used as pressing means. The pressing force of the pressing means determined by the dimensioning of the adapting ring and the springing force of the spring ring is so dimensioned that the inner mount part is reliably held in position even when mechanically loaded, e.g., when transported. The forces which act exclusively in axial direction when fixing the inner mount ring prevent the possibility of improper alignment when fixing.
The counterforce which is applied during adjustment and is generated by the piezoelectric translators is smaller than the pressing force so that the inner mount part is always pressed against the inner plane face by axial forces and cannot slip in the outer mount part in an undefined manner. A displacement first comes about under radially acting forces by means of radially acting adjusting elements.
The choice of adjusting elements to be used has a considerable influence on the reproducibility of the adjustment, on the sensitivity of the adjustment and on the possible adjustment path and ease of use. Four adjusting elements are advantageously arranged so as to be offset relative to one another by 90°. Since the adjusting elements are not intended to perform a holding function in the apparatus according to DE 44 00 869 and the axial pressing force to be overcome during the adjustment is small, the use of piezoelectric translators as adjusting elements proves particularly advantageous.
An apparatus according to DE 44 00 869 is not suitable for the relative adjustment of two optical components forming an assembly or for adjusting the assembly relative to a reference base. e.g., the optical axis of a high-performance objective.
A monolithic mount for a lens is known from DE 10 2008 029 161 B3. It comprises an annular disk which is divided by means of slits into an inner mount part and an outer mount part which preferably remain connected to one another at three locations. The persisting connections, whose geometric shape and size can be configured in different ways in principle by the position and shape of the slits, determines the possible adjustment path and the sensitivity of the adjustment. According to DE 10 2008 029 161 B3, the connections are formed by bent levers comprising two members which are connected to one another at one end by a flexure bearing and together form an angle greater than 90° and less than 180°, the other ends thereof being connected to the outer and inner mount part, respectively, by flexure bearings. The flexure bearings are portions of narrowed diameter formed by the shape and arrangement of the slits. By applying force to the connections (or manipulator units) the inner mount part can be displaced and rotated relative to the outer mount part within a plane. Monolithic mounts having manipulator units constructed in different ways are known, e.g., from EP 1 577 693 A2 and DE 10 2007 030 579 A1. The geometry of the manipulator units (shape and dimensioning) determines the possible adjustment path and sensitivity of the adjustment.
A device according to DE 10 2008 029 161 B3 is also unsuitable for the relative adjustment of two optical components forming an assembly or for adjusting the assembly relative to a reference base. e.g., the optical axis of an optical system.